1. Field of the Invention
The present invention relates to a process for introducing a carboxyl group to an aromatic carboxylic acid or a derivative thereof. More particularly, the present invention is concerned with a process for introducing a carboxyl group to an aromatic carboxylic acid or a derivative thereof by reacting an aromatic carboxylic acid or a derivative thereof with a carbon tetrahalide in the presence of a cyclodextrin and an alkali metal hydroxide. By the process of the present invention, desired aromatic polycarboxylic acids or derivatives thereof can be easily obtained with high selectivity, which are commercially valuable raw materials for polyester films, resins and fibers; polyarylate films, resins and fibers; aramid films, resins and fibers; high molecular weight and low molecular weight compounds for various types of liquid crystals; agricultural chemicals; pharmaceuticals; and dyes.
2. Discussion of Related Art
For the production of aromatic polycarboxylic acids, known is a process which comprises oxidizing an aromatic hydrocarbon substituted with an alkyl group. However, this conventional process requires stringent conditions, for example, a high reaction temperature such as 160.degree. C. or higher, a high reaction pressure such as 10 atm or higher, a large amount of a cobalt and a manganese catalyst, and a long residence time such as 20 hours or more. Further, this process is restricted in raw materials. For example, this process requires expensive raw materials, that is, paraxylene for producing terephthalic acid, metaxylene for producing isophthalic acid, 4,4'-dimethylbiphenyl for producing 4,4'-biphenyldicarboxylic acid, and 2,6-dimethylnaphthalene for producing 2,6-naphthalenedicarboxylic acid.
Also known is another process in which potassium benzoate is first produced from benzoic acid and then, the produced potassium benzoate is converted to dipotassium terephthalate and benzene by disproportionation. However, this process must also be conducted under stringent conditions, such as a temperature as high as 430.degree. to 440.degree. C., and a carbon dioxide pressure as high as 5 to 20 atm, using cadmium benzoate and zinc benzoate as catalysts. Therefore, it is difficult to control the reaction conditions and to handle the potassium salt.
In order to solve the problems accompanying the above-mentioned conventional processes for producing aromatic polycarboxylic acids, a technique in which a carboxyl group is directly introduced to an aromatic ring, has been proposed. For example, there are known the Kolbe-Schmitt reaction and the Reimer-Tiemann reaction, both of which are electrophilic aromatic substitution reactions. However, it is well known that those electrophilic aromatic substitution reactions have the following serious disadvantages: When either a hydroxyl group (--OH) or an amino group (--NH.sub.2) is present as a substituent in an aromatic ring, the substitution reaction easily occurs at the ortho- or para-position relative to the hydroxyl group or the amino group, because the hydroxyl group or the amino group acts as a strong activating group in the electrophilic aromatic substitution reaction. On the other hand, when an aromatic ring contains either a carboxyl group or a carboxylic ester group as a substituent but contains neither a hydroxyl group nor an amino group as a substituent, either the carboxyl group or the carboxylic ester group acts as a strong deactivating group in the electrophilic aromatic substitution reaction, so that it is extremely difficult to directly introduce a carboxyl group to the aromatic carboxylic acid. In fact, there has been no report on the direct introduction of a carboxyl group to the aromatic carboxylic acid [see "Yuki Kagaku (I) (Organic Chemistry Vol I)", Third edition, p.428-431, written by Morrison-Boyd, translated by Nakanishi et al., and published by Tokyo Kagaku Dojin, Japan].
Further, when a hydroxyl group or an amino group is co-present with a carboxyl group in a starting aromatic carboxylic acid, a carboxyl group to be introduced to such a starting aromatic carboxylic acid exhibits a substitution orientation for the ortho- or para-position relative to the hydroxyl group or the amino group, due to the strong activity of the hydroxyl or the amino group in the electrophilic aromatic substitution reaction. Therefore, it is impossible to obtain from such a starting aromatic carboxylic acid an aromatic polycarboxylic acid having a carboxyl group additionally introduced to an aromatic ring thereof at a position remote from the meta-position relative to the carboxyl group which is originally attached to the starting aromatic carboxylic acid.